Problems And Prospects Of Carbonaceous Reducing Agents In .
Problems and prospects of carbonaceousreducing agents in ferro alloys productionM. SubramanianC. N. Harman*ABSTRACTThe paper emphasizes the need for development of special carbon reductants for ferroalloy production. Various physical and chemical properties desired for the carbonaceous reductants are discussed as compared to their present availability and usage in ferro-alloy production.Establishment of LTC coke plant based on washed coals and production of formed cokeshould be considered to meet the requirement of ferro-alloy industry. Washed coal with lowphosphorus and ash contents will not only help in producing quality ferro alloys but also contribute to energy conservation measures.IntroductionCarbonaceous reducing agents constitutean important feed material in the production ofCr203 etc. are very high exceeding 1250 C andtherefore the use of carbonmonoxide generatedis of no use in the smelting process :tonnage ferro alloys such as High carbon ferromanganese, High carbon ferro chrome, FerroMO C -- -M COSilicon, Silico chrome and Silico Manganese etc.The reaction between CO and MO to formSince the by-product under size screened cokesCO2 is not feasible inside the electric smeltingfrom blast furnaces were available from the steelfurnace.plants at the time of the setting up of severalferro manganese plants in India during 1950"sMO CO M CO2usage of these cokes were practised and areThis is because any CO2 formed in presencebeing continued in the production of High car-of carbon becomes unstable above 1100 C andbon ferro manganese. As these contain high ashcontent, they cannot be used in Ferro siliconconsequently the reaction between cabondioxide and carbon forming carbonmonoxideproduction and therefore charcoal is being used.becomes predominant above 1100 C.The main role of the carbonaceous reducing agent in the ferro alloys is to reduce oxideores into its elements by carbon. Due to thermodynamic considerations the reduction temperature involved to reduce the oxides MnO, Ferro Alloys Corporation Ltd., Shreeramnagar.CO, C 2 COThus the otherwise useful potential heatand reducing power of the carbonmonoxide isnot useful in submerged arc furnaces and leavethe furnace unutilised. The carbonmonoxidegenerated at best would reduce the higher oxide133
like Mn02 upto the lower oxide stage Mn20d andMnO. Due to the above theoretical considerations the requirement of chemical and physicalproperties of carbon reductants are different forthe production of ferro alloys.The requirements of carbonaceous reducingagents also depends on the nature of processinvolved in ferro alloy production. It can becategorised into two types namely for the production of ferro alloys where slag is formed asa by-product and those where no slag is formed .In the first category the production of Highcarbon ferro manganese, High carbon ferrochrome, silico chrome, silico manganese etc.,can be included. In the second category, Ferrosilicon, Silicon metal and Calcium silicide areincluded. This distinction in the process technology makes it necessary to use a very reactiveand a very low ash containing carbonaceousreducing agent for the production of ferro siliconand silicon metal as compared to other ferroalloys. As special type of carbonaceous reducing agent containing low ash and low phosphorus is not produced in India, charcoal isused as reducing agent.In the case of slag making processes a certain amount of ash content can be toleratedsince this can be fluxed along with the gangueof the ores with suitable fluxing agent like limestone and dolomite. In view of this, B. P.Metallurgical nut and pearl cokes obtained fromsteel plants are used in the production of Highcarbon ferro manganese.Physical and Chemical Properties ofReducing agentsFixed CarbonThe fixed carbon in the reducing agentshould be as high as possible but not less than85%. Any lower fixed carbon in the carbonaceous reducing agents means high ash contentor volatile matter and will contribute to moreslag volume resulting in increased power consumption per tonne of alloy produced and highPhos content in the metal.134Volatile MatterThe presence of volatile matter in the reducing agents contributes to higher reactivity.However, it should not be at the expense of thefixed carbon level. Recently in view of the nonavailability of low phos cokes or special reducing agents some amount of non-coking coalsto an extent of 20 to 30% of the total fixedcarbon required are used in the production ofHigh carbon ferro manganese, High carbon ferrochrome 8. Ferro silicon. The volatile matterreleased, on heating, oxidises above furnacecharge and produces intense heat. This leadsto severe heating of furnace super structure byradiation and resulting in water leakages fromthe pipe joints as well as from the contactclamps. Further, condensation of tar productson electrode clamps and other furnace parts,causes serve corresion problem leading to expensive maintenance and unproductive shutdowns. Therefore, the use of non-coking coalsexcept for nominal requirements should not bepractised. However, in view of the non-availability of other cokes having Low phos content,most of the ferro alloy units in India use somequantity of non-coking coals containing highash content of the order of 16 to 20% andvolatile matter 30 - 35%. In principle the noncoking coals get devolatilised and transforms tolow temperature carbonised char during thedescent to the lower part and takes part in thereduction while the volatile matter simplyescapes to the atmosphere after burning. It isworthwhile to note that if suitable low ash noncoking coals are made available, this can beused to an increased amount. The design of thefurnace needs suitable modification to accommodate the high volatile matter released by incorporating waste heat boilers and gas cleaningequipments.Ash ContentThe ash content should be low since itrepresents impurities and contributes to higherslag volumes. Each 1% of ash content in cokewill increase slag volume by about 10 to 15 kg
per tonne of ferro alloy which in consequencewill consume more electric power for its smelting and removal es slag apart from metal lossesto slag.In the production of Ferro Silicon andSilico Chrome high ash content leads to itsfusion and coating of the quartz (source ofsilicon) with slag. It hampers the progress ofreaction, causes more slag formation and disrupts the operation by frequent crust formationand severe blows. It also increases Al contentof the ferro silicon. Therefore the ash contentshould be 8-12% maximum .SulphurSulphur content of carbon reductant in theusual range of 0.6 to 0 8% in the productionof High carbon ferro manganese or Ferro siliconis not a severe problem because most of it getsvolatilised due to high temperature of operationand also gets eliminated in the slag containingmanganese. Generally sulphur content of IndianCoals/Cokes is low compared with foreigncarbon reductants. However, the sulphur content in High carbon ferro chrome and ChargeChrome has to be kept at 0.03% max, since itis difficult to remove it in stainless steel making.Therefore, care must be taken to avoid coal andcoke with higher sulphur content such as rawpetroleum coke which contains 3 to 4%.PhosphorusThe most undesirable constituent in carbonreductants is phosphorus. About 70 - 80% ofthe phos input gets reduced and alloyed withthe ferro alloy produced. Since ferro alloys areused at the finishing stages of various alloy andstainless steel production, phos cannot be decreased once it is introduced through ferro alloy.Therefore 'P' content in reductants should be0.02% maximum.Problems of phos in high carbon ferromanganese Et silico manganese .During the last few years the availability ofby-product metallurgical cokes or beehive hardhave become poor, the cost has becomeexorbitant while the quality has deteriorated verymuch. The ash content is about 28 to 30%,Phos content has gone up to 0.17 to 0.19%.It should be noted that the usage of Manganeseores with high phosphorus, has become thecokesorder of the day and this has necessitated to lookfor other carbonaceous reducing agents containing low ash and low phos.While the Indian Standard Specification forHigh Carbon Ferro Manganese has increasedphos to 0.4% max still many steel plants areusing 0.35 max phos and thus the use of lowphos containing coke is essential for productionof High carbon ferro manganese. If high carbonferro manganese is to be exported then phoslevel should be 0.25 max and this requires a verylow phos containing carbon reductant. It shouldbe noted that the phosphorus removal in SteelPlants requires extended time of refining, additional amount of fluxes, and energy consumption.All these can be minimised by using low Pcokes in ferro manganese production and supplying low P containing ferro manganese forsteel plants.Since major manganese ores are availablein the country are siliceous, these are suitablefor Silico manganese production. But due tohigher phos content, the use of silico manganese has not been considered by the steel makersin India, as compared to the advanced countrieslike U.S.A., Japan and other European countrieswhere almost 50% of manganese is used inthe form of silico manganese. Further. theferro manganese slag containing high manganese with low phos 0.03% max which is obtainedas By-product during the production of Highcarbon ferro-manganese can also be utiiised inthe production of Silico-manganese. Thus ifrequisite quality of low phos metallurgical cokesare available, the production and use of silicomanganese can be adopted which will not onlyhelp in conservation of valuable manganeseresources but also help in the yield and qualityof the final steel products.135
Phosphorus in charge chromeSince Charge Chrome is mainly used in theproduction of stainless steels, high chromiumalloy steels, super alloy steels, requiring highcorrosion resistance and toughnes, the phoscontent should be extremely low. Therefore, thespecification for Charge chrome with reference tophosphorus is very stringent. Most of theChargechrome producers abroad make use ofgas coke or other special carbon reductantscontaining very low ash content, and phos notexceeding 0.015%. The phosphorus content,in Silico Chrome also should be low as this isused in the production of low carbon ferrochrome and Extra low carbon ferro chrome.Therefore, it has become paramount importancenow. to have a suitable carbonaceous reducingagent similar to that of cokes available abroadfor using it in the production of ferro chromealloys.Physical PropertiesIn Electric furnaces, the carbon reductantsnot only serve as reducing agents but also asconducting material for the passage of electricalcurrent and contributes to ohmic resistance.Deep penetration of the electrodes is required toensure smooth functioning of the furnace andhigh recovery of metals like silicon. The production of Ferro silicon and Silico Chrome requirescokes of high reactivity and high electrical resistance.Since the electrical resistance is a factordepending on the porosity, particularly themicro-porosity of coke and since the reactivityof coke increases with an increasing internalsurface area, a specifically light coke is neededboth from the point of view of reactivity andhigh electrical resistance.For these reasons the coke should be lightcharcoal with high porosity.The following is specified :1) Apparent specificgravity136: 0.8 gm/cc2) Bulk density: 450 - 500 kg/m3 for10 - 40 mm size.3)Porosity: 25 - 35%4)Though very high strength as that requiredfor cokes used in blast furnaces are notnecessary in electric furnaces due to itssmall height, it should be high enough towithstand transport and mechanical handling operations and to lead to minimumgeneration of fines of less than —6 mm.5)The fusion point of the ash should be highso that it will not melt at low temperatureand cause surface coating of the raw materials and impair the reduction of oxides bypromoting slag formation. In Ferro Alloyproduction, the main reduction takes placein solid state between ore and carbon exceptin Mn alloy production.6)Electrical resistivity : Specific electricalresistance should be70 - 100 Ohm cm/cm'(measured at roomtemperature7 - 15 mm size)Reactivity of Special Carbon ReductantsThe concept of reactivity of carbon reductants is some what different in ferro alloy production. Originally metallurgical cokes wereused where reactivity was understood as the rateof combustion with oxygen. Since metallurgical coke is used in blast furnaces and cupolawhere it is oxidised with air from tuyeres, theusual determination of reactivity by critical airblast method or CO2 method, is useful enough.But in ferro alloy production especially ferrosilicon and silicon containing ferro alloys, thereactions involved are different since formationof silicon monoxide constitute an importantintermediate reaction gas amounting to aboutan equal proportion as that of carbon monoxide.The SiO raising from bottom of the electrodesdisproportionates by condensation into Si metal,plus Si02 at the less hotter top portions. Alsoit reacts with carbon to form silicon carbide
which again reacts lower down with Si02 tocountries gas cokes and special carbon reductants such as Rexco Semi-coke, Auschar, etc.,form Silicon Metal.with low ash content and low phos. are used inTherefore, the carbon reductants must haveferro aloy production, such special cokes withthe ability to promote the condensation reactionhigh reactivity are not available in India andwhich ascends at a fast velocity from the furna-therefore wood charcoals are mainly used espe-ces. Otherwise there will be great loss of sili-cially in Ferro Silicon production. However,con. Usually the silicon recovery is about 80the charcoals obtained from different areas con-percent only in ferro silicon production and thustain varying proportions of volatile matter due toabout 20 percent of silicon is lost as SiO whichimproper carbonisation, and phosphorus due toimmediately oxidises to submicron size silicathe types of wood used and the soil from whichfumes on contact with infilterated air in openthe trees are grown. The charcoal is very fragileand semi closed furnaces. This leaves as denseand generates considerable under size rejectswhite fumes from furnace chimneys.during loading and unloading operations, transportation, storage etc. Due to its high adsorp-Reactivity Measurementstion property, it contains very high moisture ifSince the concept of reactivity is differentfor Blast furnace cokes and carbonaceous redu-exposed to rains. Also it being very reactive,oxidises faster on the surface of the charge andcing agents used for ferro silicon alloys, severaltheretore a higher fixed carbon will be requiredmethods have been evolved for determination ofper tonne of Ferro silicon.reactivity such as SINTEF. Norwegian technicalUniversity of Trontheim has evolved a methodcalled SINTEF METHOD for determining the SiOreactivity of various carbon reductants. In thistest, a known mixture of SiO and CO is allowedto flow by use of Argon as a carrier gas at1650 C over a 20 cm3 sample of material ofgrain size —6.35 4 mm. The reactivity num-It may be mentioned that in slag formingprocesses such as high carbon ferro chrome orchargechrome, high carbon ferro manganeseetc, such high SiO reactivity values are notrequired.Moistureber is measured in ML of SiO gas left unutilisedHigh moisture content disturbs the carbonduring reaction. Several carbonaceous reducingbalance. Uniformity in moisture content is moreagents have been measured by this method andimportant without frequent or sudden variations.the values are indicated as follows : the RexcoHigh moisture content results in higher require-Semi coke is ranging from 950 to 1200 ML onthis scale, charcoal in 450 - 700 ML range, meta-ments of fixed carbon and also power consump-llurgical coke in 1500 — 2000 ML and petroleumpower for evaporation, but also consumescoke and Anthracite 2000 — 2500 ML range.carbon from electrode and carbonaceous reduc-tion. Moisture not only consumes electricing agents.The reaction 2C SiO (gas) SiCCOC H20 - CO H2(gas) is very important above the temperature1520 C. The more reactive the coke, the lesssilicon monoxide gas will escape through thefurnace. SiO gas from furnace also containsintense electrical heat energy By using a carbonreductant of high surface area and reactivity, thepower consumption per ton of ferro silicon canUsually the Hydrogen content goes up in thefurnace gases if water leakages are there ormoisture in coke is very high.Silicon monoxide also reacts with H2O toformbe brought down and increased recovery of silicon can be obtained. While in Norway and otherSiO H2O - SiO2 H2137
The above two reactions are endothermicand therefore results in excess power consump-up suitable plants to produce special carbonreductants.tion in ferro silicon production. The moisturecontent should be uniform and should be maximum 4.0% in B. P. Cokes, coals etc , In lighterTalcher and Singareni coalfields are havingabundant reserves of non coking coals. Thesuperior grade coals can be earmarked for con-types like charcoal it should be 8.0% max.version into special cokes for electro metallurAfter having briefly reviewed the necessitygical industries.for using special carbonaceous reducing agentsThe following steps are worth considering :the chemical and physical properties desired forferro alloy production is indicated in Table.1)TABLESince the quantum of coal required forspecial coke production is not much, miningChemical & Physical Properties desired forof low P, low ash coals from Bottom Sec-carbon reductantstions of the basal seam in Talcher and otherFixed carbonVolatile matterAshPhoscoal fields should be pursued and intensified.85% Min (drybasis)3% max12% max0.015% max2)The mined coal should be segregated withregard to low phos and ash content and reser-VISulphur0 6% maxved for ferro alloy production and the bala-Moisture6.0% maxnce only should be alloted to thermal powerSizeBulk density10 - 40 mm5%400 - 500 kg/m3Ash fusion point C1250 - 1450 stations, railways, fertilisers, cement, paperand other industries where it is used as fuel.As compared to the total demand estimateof about 9 million tonnes of Talcher coalRequirements of Carbonaceous Reducingduring 1984-85 and about 28 million tonnesAgentsduring 1989-90, the demand for makingspecial cokes would be 0.6 millions onlyThe requirement of carbonaceous reducingper annum. This can be reserved from theagents for Ferro Alloy industry in India wouldcoal production from the underground mineamount to about 6,00,000 tonnes which is basedin Talcher.on an average 70% fixed carbon, 10% moisture,15% rejects due to handling loss and under3)As the demand for coal for production ofsize materials. In actual practice this will bespecial cokes is not much as compared tomuch more due to wide variation in the abovethe overall demands, setting up of suitableparameters. However, if special carbonaceouscoal washeries would be highly rewarding.reducing agents are used, there will be less con-To obtain 0.6 million tonnes, assuming 25%sumption.rejects as middling and waste, a washerycapacity of 0.8 million is required with aAs compared to Blast furnaces, wheredaily capacity of 3000 tonnes per day.large quantities of metallurgical coke areDepending on the economics, either two orrequired, the amount required for ferro alloys isthree coal washeries can be set up at diffe-not much. For instance for the newly proposedrent locations. The main objective of thisVisakhapatnam Steel Plant, the coke requirementwashery would be to bring down the ashwould be 2.2 million tonnes for 3.4 millionless than 8.0% and P to less than 0.010%tonnes of ingot steel capacity. Thus it can beseen that it is not beyond the means of the coalauthorities or other Government agencies to set1384)There was some proposal to set up a formedcoke plant
the ferro alloy produced. Since ferro alloys are used at the finishing stages of various alloy and stainless steel production, phos cannot be dec-reased once it is introduced through ferro alloy. Therefore 'P' content in reductants should be 0.02% maximum. Problems of phos in high carbon ferro manganese Et silico manganese.
the practice of making waste-load allocations from models that contain both a BOD 5 (assumed to be a measure of the carbonaceous demand) and a nitrogenous demand. The severity of the problem is illustrated in Figs. 1 and 2. Figure 1 compares the effluent BOD 5 with the CBOD 5 (carbonaceous component of the BOD 5). The CBOD 5 is determined by
Related U.S. Application Data a syngas includes: providing a plasma heated carbonaceous (62) pyi - - - of applit o : 3. 9,813, filed on Sep. bed deposited in a bottom feed section material of on a reactor top of vessel; the carbonaceous forming a bed bed; of s , now Fal. No. 9, UU).3 ZU.
FAO FORESTRY PAPER FAO FORESTRY PAPER 171 171 FAO Edible insects: future prospects for food and feed security 171 Edible insects Future prospects for food and feed security Edible insects Future prospects for food and feed security I3253E/1/04.13 ISBN 978-92-5-107595-1 ISSN 0258-6150 9 789251 075951
World population prospects The 2015 revision, key findings & advance tables (2015) The world population situation in 2014 (2014) Situation de la population mondiale en 2014 . World urbanization prospects 1990 (1991) United Nations world population chart 1990 (1990) World population prospects (1989) Prospects of world urbanization 1988
1 Problems: What is Linear Algebra 3 2 Problems: Gaussian Elimination 7 3 Problems: Elementary Row Operations 12 4 Problems: Solution Sets for Systems of Linear Equations 15 5 Problems: Vectors in Space, n-Vectors 20 6 Problems: Vector Spaces 23 7 Problems: Linear Transformations 28 8 Problems: Matrices 31 9 Problems: Properties of Matrices 37
CHEMICAL KINETICS & NUCLEAR CHEMISTRY 1. Theory 2. Solved Problems (i) Subjective Type Problems (ii) Single Choice Problems (iii) Multiple Choice Problems (iv) Miscellaneous Problems Comprehension Type Problems Matching Type Problems Assertion-Reason Type Problems 3. Assignments (i) Subjective Questions (ii) Single Choice Questions
PROBLEMS AND PROSPECTS OF TEACHING CHEMICAL EQUILIBRIUM AT THE FURTHER EDUCATION AND TRAINING (FET) BAND by GODFREY PISIRAI MARUMURE Submitted in accordance with the requirements . Classification of Experiment/ Demonstration and Concept Applied 54 13. Categories of Problems/ Challenges when teaching Chemical Equilibrium 56 viii .
P 4 418.668 P 4 419.989 P 5 418.186 P 5 419.227 P 6 418.973 P 6 419.684 P 7 419.379 P 7 420.751 P 8 420.141 P 8 420.065 P 9 419.532 P 9 421.259 P 10 418.643 P 10 421.386 P 11 418.719 P 11 418.846 P 12 416.763 P 12 419.887 P 13 414.782 P 13 418.363 P 14 P 14 P 15 P 15 P 16 P 16 P 17 P 17 P 18 P 18 P 19 P 19 Test Sample j 2 Test Sample j 3 Reading Points Reading Points Reading Points Test Sample .
